Luminous body, electron beam detector using the same, scanning electron microscope, and mass analysis device

ABSTRACT

A light-emitting body of rapid speed of response and high light emission intensity, and an electron beam detector, scanning electron microscope and mass spectroscope using this are provided. In the light-emitting body  10  according to the present invention, when fluorescence is emitted by a nitride semiconductor layer  14  formed on one face  12   a  of a substrate  12  in response to incidence of electrons, at least some of this fluorescence is transmitted through this substrate  12 , whereby that fluorescence is emitted from the other face  12   b  of the substrate. The response speed of this fluorescence is not more than μsec order. Also, the intensity of emission of this fluorescence is almost identical to that of a conventional P47 phosphor. Specifically, with this light-emitting body  10 , a response speed and light emission intensity are obtained that are fully satisfactory for application to a scanning electron microscope or mass spectroscope. In addition, a cap layer  16  contributes to improvement in the persistence rate of light emission in the nitride semiconductor layer  14 , so, with this light-emitting body  10 , not only high-speed response and high light emission intensity are obtained, but also an excellent persistence rate.

This is a continuation application of application Ser. No. 11/547,807,having a §371 date of Sep. 6, 2007 now U.S. Pat. No. 7,910,895, which isa national stage filing based on PCT International Application No.PCT/JP05/006870, filed on Apr. 7, 2005. The application Ser. No.11/547,807 is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a light-emitting body that emits lightin response to incidence of electrons, an electron beam detector, ascanning electron microscope and a mass spectroscope using thelight-emitting body.

BACKGROUND ART

Conventional electron beam detectors, when measuring an electron beam ofstrong intensity, perform detection of the electron beam by measuringthe current value produced by the electron beam, but, in the case ofmeasurement of an electron beam of comparatively low intensity, theamount of charge produced by the electron beam is small, so it is notpossible to detect the electron beam efficiently. Accordingly, in thecase of an electron beam detector used in for example a scanningelectron microscope (SEM), measurement is conducted by irradiating asample surface with the electron beam, collecting the secondaryelectrons generated at this sample surface and using these to irradiatea phosphor, and detecting the fluorescence generated by this phosphorusing a photomultiplier tube (photodetector). As such phosphors, thevarious types of phosphor shown in FIG. 9 are known; this table showsthe phosphor, response speed, light emission intensity, lifeperformance, light emission wavelength, and material (photoelectricsurface) of the fluorescence detector. The order of excellence in thistable is indicated by the symbols: double circle, circle, triangle, andcross.

In recent years, in the field of scanning electron microscopes or massspectroscopes, phosphors are being demanded that provide high lightemission intensity and fast response speed. The reason for this is thatfor example in the case of a scanning electron microscope, if the speedof response of the phosphor is fast, the scanning speed can consequentlybe made fast, making it possible to improve the performance of theequipment.

-   -   Patent reference 1: International Laid-open Patent Application        No. 02/061458 pamphlet

However, in the case of a conventional phosphor as shown in FIG. 9,there was the problem that it was difficult to obtain a fast responsespeed (of the order of μsec) sufficient for a scanning electronmicroscope or mass spectroscope. It should be noted that, of the smallnumber of phosphors with which a good response speed is obtained, GaAsPlight-emitting bodies have a low intensity of light emission and so wereunsuitable for application to scanning electron microscopes and thelike.

DISCLOSURE OF THE INVENTION

The present invention was made in order to solve the problem describedabove, its object being to provide a light-emitting body of fastresponse speed and high intensity of light emission, and an electrondetector, a scanning electron microscope and mass spectroscope usingthis.

In a light-emitting body that emits fluorescence in response toincidence of electrons, a light-emitting body according to the presentinvention comprises a substrate, a nitride semiconductor layer having aquantum well structure formed on one of the faces of the substrate, anda cap layer having an electron incidence face that is formed on thenitride semiconductor layer. Specifically, this light-emitting body is alight-emitting body that converts incident electrons to fluorescence andcomprises: a substrate that is transparent to this fluorescence; anitride semiconductor layer having a quantum well structure that emitsfluorescence in response to incidence of electrons, that is formed onone of the faces of the substrate; and a cap layer that is formed ofmaterial of larger band gap energy than the constituent material of thenitride semiconductor layer.

In this light-emitting body, when the nitride semiconductor layer formedon one face of the substrate emits fluorescence in response to incidenceof electrons, at least some of the fluorescence passes through thesubstrate and is emitted from the other face of the substrate. Thisfluorescence is caused by recombination of pairs of electrons andpositive holes that are formed by incidence of electrons onto thequantum well structure of the nitride semiconductor layer and itsresponse speed is of μsec order or less. Also, the intensity of lightemission of this fluorescence is of the same order as a conventional P47phosphor.

That is, this light-emitting body has sufficient response speed andlight emission intensity for application to a scanning electronmicroscope or mass spectroscope. Also, the cap layer contributes to animprovement of the rate of persistence of light emission in the nitridesemiconductor layer, so not only are high-speed response and high lightemission intensity achieved with this light-emitting body, but also anexcellent persistence rate is achieved. The “persistence rate” is avalue expressing the degree to which the light emission intensitypersists after lapse of a prescribed time and may be expressed forexample as a percentage obtained by dividing the light emissionintensity after lapse of a prescribed time by the original lightemission intensity.

Also, preferably the well width of the quantum well structure is notmore than 4 nm. In this case, a light-emitting body that emitsfluorescence of at least the desired amount can be obtained.

Also, the thickness of the cap layer is preferably not more than 10 nm.In this case, the response speed of the light-emitting body as a wholeis improved by reducing the light emission component of the cap layer.

Also, preferably the nitride semiconductor layer is constituted of InGaNand GaN, and the cap layer is constituted of AlGaN. In this case, thecap layer is constituted of a material of larger band gap energy thanthe constituent material of the silicon nitride semiconductor layer.

Also, preferably there is further provided a reflective film laminatedon the cap layer. In this case, the persistence rate may be furtherimproved by this reflective film.

Also, preferably the thickness of the reflective film is at least 800nm. In this case, a better persistence rate can be obtained.

An electron beam detector according to the present invention ischaracterized by the provision of the light-emitting body and aphotodetector having sensitivity for fluorescence emitted by thislight-emitting body.

In this electron beam detector, measurement of an electron beam isperformed by directing the fluorescence emitted from a light-emittingbody as described above onto the optical incidence face of aphotodetector. Specifically, measurement of the electron beam isperformed by means of the fluorescence, which is produced with the fullysufficient response speed and light emission intensity that is required.Also, since the light-emitting body has an excellent persistence rate,the life performance in this electron detector is significantlyimproved. Also, by employing this electron beam detector in a scanningelectron microscope or mass spectroscope; the performance of thismicroscope etc can be improved.

A scanning electron microscope according to the present invention ischaracterized in that it comprises: an electron beam detector comprisingthe light-emitting body and a photodetector having sensitivity for thefluorescence emitted by this light-emitting body; and a vacuum chamberwherein at least the light-emitting body is arranged, and in that animage of a sample is picked up by scanning the surface of the samplearranged in the vacuum chamber with the electron beam, whereby directingthe secondary electrons generated from the sample onto the electrondetector and then correlating the scanning position of the sample andthe output of the electron beam detector.

A mass spectroscope according to the present invention is characterizedin that it comprises an electron beam detector comprising thelight-emitting body and a photodetector having sensitivity for thefluorescence emitted by this light-emitting body; a vacuum chamberwherein at least the light-emitting body is arranged; a separatingsection for separating in spatial or time-wise fashion the ionsgenerated from a sample in the vacuum chamber in accordance with theirmass; and a dynode that is irradiated with the ions separated by theseparating section, secondary electrons generated from the dynode inresponse to incidence of ions on the dynode being directed to theelectron detector, mass spectroscopy of the sample being performed fromthe output of the electron beam detector.

According to the present invention, a light-emitting body of fastresponse speed and high light emission intensity and an electron beamdetector, a scanning electron microscope and mass spectroscope usingthis are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a light-emitting body accordingto an embodiment of the present invention.

FIG. 2 is a graph showing the response characteristic of alight-emitting body having an InGaN/GaN quantum well structure.

FIG. 3 is a graph comparing the amount of light emitted by alight-emitting body having an InGaN/GaN quantum well structure and aconventional light-emitting body.

FIG. 4 is a graph showing the relationship between metal backing layerthickness and persistence rate for various cap layer thicknesses.

FIG. 5 is a graph showing the relationship between well width and amountof light emitted by a light-emitting body having an InGaN/GaN quantumwell structure.

FIG. 6 is an axial cross-sectional view showing an electron beamdetector according to an embodiment of the present invention.

FIG. 7 is a layout diagram showing a scanning electron microscope usingan electron beam detector according to FIG. 5.

FIG. 8 is a layout diagram showing a mass spectroscope using an electronbeam detector according to FIG. 5.

FIG. 9 is a table showing the properties of a conventional phosphor.

-   10 light-emitting body-   12 substrate-   14 nitride semiconductor layer-   16 cap layer-   18 metal backing layer-   20 electron beam detector-   22 optical member-   30 photodetector-   AZ separating section-   DY1, DY2 dynode-   e1, e2, e3 electron beam-   I light incident face-   SM sample.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A mode that is believed to be optimum in implementation of alight-emitting body, and an electron beam detector, a scanning electronmicroscope and mass spectroscope using this according to the presentinvention are described below in detail with reference to the appendeddrawings. Elements which are the same or similar are indicated by thesame reference symbols and where the description would be duplicatedsuch description is dispensed with.

As shown in FIG. 1, a light-emitting body 10 comprises a base 12, anitride semiconductor layer 14 formed on the substrate surface 12 a, acap layer 16 and metal backing layer (reflective film) 18 successivelylaminated on the nitride semiconductor layer 14. Attracted by thepositive potential applied to the metal backing layer 18, electrons aredirected onto the metal backing layer 18. Since the metal backing layer18 has a thickness capable of transmitting electrons, electrons areincident on the interface (electron incidence face) between the metalbacking layer 18 and the cap layer 16 and enter into the interior.

The material of the substrate 12 is an insulator of extremely large bandgap energy being made of transparent sapphire (alumina: Al₂O₃), which isof low absorption rate for light of wavelength of 170 nm or more.Specifically, the insulating substrate 12 has the property oftransmitting light of wavelengths of about 170 nm or more. The nitridesemiconductor layer 14 is a three-layer structure in which, from theside of the substrate 12, a buffer layer 14A of In_(x)Ga_(1-x)N (0≦x≦1),a GaN layer 14B doped with Si, and a quantum well structure layer 14C ofInGaN/GaN are successively laminated. This InGaN/GaN quantum wellstructure layer 14C is a layer having a quantum well structureconstituted by InGaN and GaN, and emits fluorescence of wavelength about415 nm when irradiated by an electron beam. Specifically, when anelectron beam is incident that reaches the quantum well structure 14C,electron/positive hole pairs are formed, and fluorescence is emitted bythe process of recombination of these in the quantum wells.

Thus, at least the portion of this fluorescence that is of longerwavelength than 170 nm passes through the substrate 12 and is emittedfrom the rear face (substrate rear face) 12 b of the substrate surface12 a. It should be noted that the “quantum well structure” referred toin the present specification, apart from an ordinary quantum wellstructure, includes a quantum wire structure or quantum dot structure.Also, in this specification, a “nitride semiconductor” is a chemicalcompound including at least one of Ga, In, or Al as group III elementand including N as the main group V element.

Next, the quantum well structure 14C of the nitride semiconductor layer14 will be described. FIG. 2 is a graph showing the responsecharacteristic of light emission of a light-emitting body having anInGaN/GaN quantum well structure and likewise showing a graph of theresponse characteristic of a GaN light-emitting body of the conventionalbulk structure for comparison. The horizontal axis of the graph of FIG.2 is the time (μsec) and the vertical axis shows the magnitude(arbitrary constant) of the response output when an electron beam in theform of a pulse is incident in the vicinity of time 0.

It can be seen from this graph that in the response characteristic ofthe InGaN/GaN quantum well structure layer 14 C, the response speed S1(width of inclination of the graph) of a light-emitting body having anInGaN/GaN quantum well structure is of nsec order, whereas the responsespeed S2 of a GaN light-emitting body of bulk structure is of 10 μsecorder. The reason why the response speed of a light-emitting body havingsuch an InGaN/GaN quantum well structure is faster than that of a GaNlight-emitting body of bulk structure is believed to be that in the caseof a light-emitting body having an InGaN/GaN quantum well structureinter-band light emission is dominant whereas in the case of a GaNlight-emitting body of bulk structure deep-layer light emission isdominant.

Also, the amount of light emitted by the fluorescence emitted from alight-emitting body having an InGaN/GaN quantum well structure wasmeasured and a comparison (see FIG. 3) of amount of light emitted(arbitrary units) with a conventional light-emitting body was made. As aresult, it was found that the amount of light emitted (average about7.20×10¹²) by a light-emitting body having an InGaN/GaN quantum wellstructure was considerably larger than the amount of light emitted(average about 4.81×10¹²) by a GaN light-emitting body of bulkstructure, and of about the same order as the amount of light emitted bya P47 light-emitting body of large amount of light emission. Also, itwas found that, compared with the amount of light emitted (9.8×10¹⁰) bya GaAsP light-emitting body with which a good response characteristicwas obtained, the light emission intensity was nearly 100 times better.

Returning to FIG. 1, the cap layer 16 of the light-emitting body 10 isof thickness 10 nm and is constructed of Al_(x)Ga_(1-x)N (0≦x≦1). ThisAlGaN that is used to construct the cap layer 16 has a band gap energythat is larger than that of the InGaN or GaN used to construct theInGaN/GaN quantum well structure layer 14C. Consequently, the pairs ofelectrons and positive holes that are generated in the quantum wellstructure layer 14C are efficiently fed to the quantum wells. That is,by adopting this cap layer 16, recombination of the electrons andpositive holes in the quantum well structure 14C is facilitated.Consequently, the brightness (amount of light emitted) is significantlyimproved compared with the conventional light-emitting body, which hasno cap layer 16.

Also, this efficient feeding of the electrons and positive hole pairsgenerated in the quantum well structure layer 14C to the quantum wellsenables the period of continuance of recombination of electrons andpositive holes to be extended. Consequently, in the case of thislight-emitting body 10, the light emission intensity continues for alonger time than in the case of a conventional light-emitting body,which has no cap layer 16. That is, with the light-emitting body 10, thepersistence rate, which is a value indicating the degree to which theintensity of light emission persists after lapse of a prescribed time,is improved. Furthermore, as a result of meticulous study, the inventorsdiscovered that, by making this cap layer 16 of small thickness, it waspossible to significantly reduce the light emission component (lightemission component in the vicinity of 550 nm) of the cap layer lightemission, thereby improving the response speed of the light-emittingbody as a whole. The thickness of the cap layer 16 is thereforepreferably not more than 10 nm.

The metal backing layer 18 is of thickness 800 nm and is constructed ofAl. By means of this metal backing layer 18, further improvement in thepersistence rate of the light-emitting body 10 can be achieved.

The relationship between the cap layer thickness and the metal backinglayer thickness will now be described with reference to FIG. 4. FIG. 4is a graph showing the relationship between the metal backing layerthickness (nm) and the persistence rate (percentage obtained by dividingthe light emission intensity after the lapse of eight hours by theoriginal light emission intensity). From this graph, it can be seen thatthe persistence rate tends to improve as the thickness of the metalbacking layer is increased. Also, it can be seen that if the thicknessof the metal backing layer is 800 nm or more, there is a marked increasein the persistence rate. That is, it is preferable that the thickness ofthe metal backing layer 18 should be at least 800 nm. In particular, ifthe cap layer 16 is 10 nm and the metal backing layer 18 is 800 nm, bothhigh-speed response and a high persistence rate (about 90%) can beachieved.

As described above, the inventors discovered that, with a light-emittingbody having an InGaN/GaN quantum well structure, a faster response speedcan be achieved than in the case of a conventional GaN substrate of bulkstructure. Also, they discovered that the amount of light emitted (lightemission intensity) by a light-emitting body having an InGaN/GaN quantumwell structure is larger than (or similar to) the amount of lightemitted by a conventional bulk structure GaN light-emitting body or P47phosphor. Also, both the response speed and light emission intensity ofa light-emitting body having an InGaN/GaN quantum well structure arefully sufficient for use in a scanning electron microscope or massspectrometer. That is, a light-emitting body 10 comprising a nitridesemiconductor layer 14 having an InGaN/GaN quantum well structure layer14C can be the to be a light-emitting body that is much more suitable asa light-emitting body for use in a scanning electron microscope or massspectroscope than conventional light-emitting bodies. Also, by adoptionof a cap layer 16 and metal backing layer 18, an excellent persistencerate of the light-emitting body 10 can be achieved.

It should be noted that, in the InGaN/GaN quantum well structure of thenitride semiconductor layer 14, preferably the well width of the quantumwells is not more than 4 nm. FIG. 5 is a graph showing the relationshipbetween the well width of the quantum well structure of InGaN/GaN of thenitride semiconductor layer 14 and the light emission intensity. Thehorizontal axis of the graph of FIG. 5 is the well width (nm) and thevertical axis is the amount of light emitted (arbitrary units) whenirradiated with an electron beam of a prescribed amount. From thisFigure, it can be seen that, whereas the amount of light emitted issmaller than 1×10¹² when the well width is 6 nm, when the well width isnot more than 4 nm, the amount of light emission is in each case atleast 1×10¹². That is, by making the well width of the quantum wellstructure not more than 4 nm, an amount of light emission of at least1×10¹² can be achieved, thereby making it possible to obtainfluorescence that is ideal for practical use from the light-emittingbody 10.

Also, regarding the combinations of materials of the substrate 12 andquantum well structure layer 14C, various other combinations apart fromsapphire and InGaN/GaN quantum well structure are possible: thesecombinations are described below. Table 1 shows substrates that aresuitable for the material of the substrate 12.

TABLE 1 Transmission Substrate material wavelength [nm] [eV] GaN 3663.39 AlN 200 6.2 LiAlO₂ (LAO) 191 6.5 LiGaO₂ (LGO) 221 5.6 ZnO 368 3.376H—SiC 409 3.03 4H—SiC 380 3.26 α-Al₂O₃ (sapphire) 170 — MgO 200 —MgAl₂O₄ 200 —

The materials shown in Table 1 are materials of comparatively shorttransmission wavelength and include materials (for example AlN) thattransmit light of the entire visible optical region.

Also, the material of the quantum well structure layer 14C can besuitably selected from nitride semiconductors having a quantum wellstructure constituted by In_(x)Al_(y)Ga_(1-x-y)N (x≦1, y≦1, x+y≦1) andIn_(a)Al_(b)Ga_(1-a-b)N (a≦1, b≦1, a+b≦1). Consequently, apart from thequantum well structure layer 14C (InGaN/GaN combination) describedabove, it would possible to employ for example a combination such asInGaN/AlGaN or InGaN/InGaN or GaN/AlGaN.

In the combinations of substrate material and quantum well structurelayer material described above, the wavelength of the fluorescence thatis emitted by the quantum well structure layer 14C must be longer thanthe transmission wavelength of the substrate 12. Specifically,fluorescence is emitted from the substrate rear face 12 b by selecting asubstrate material of transmission wavelength that is shorter than thewavelength of the fluorescence that is emitted by the quantum wellstructure layer 14C or by selecting a material for the quantum wellstructure layer 14C that emits fluorescence of wavelength longer thanthe transmission wavelength of the substrate 12.

Next, a method of manufacturing a light-emitting body 10 as describedabove will be described.

In the manufacture of a light-emitting body 10, first of all, a sapphiresubstrate 12 is introduced into the deposition chamber of an organicmetal vapor phase deposition device (MOCVD) and heat treatment performedfor five minutes at 1050° C. in an atmosphere of hydrogen, to clean thesapphire substrate surface 12 a. The temperature of the substrate isthen lowered to 475° C., and an InGaN buffer layer 14A of thickness 25nm is deposited; the temperature of the substrate is then raised to1075° C., to grow a GaN layer 14B of 2.5 μm. After this the temperatureof the substrate is lowered to 800° C. to form a quantum well structurelayer 14C of In_(x)Ga_(1-x)N (x=0.13)/GaN. The thickness (well width) ofthis InGaN/GaN quantum well structure 14C is 2 nm, the number of wellsin the barrier layer 10 nm is 11, and the well layer and barrier layerare doped with 1.8×10¹⁸ cm⁻³ of Si. It should be noted that the numberof wells is not restricted to 11, and could be suitably adjusteddepending on the accelerating voltage of the incident electron beam.Also, the thickness of the barrier layer is not restricted to 10 nm andcould be any thickness such that the electrons are satisfactorilyenclosed in the well layer.

A cap layer 16 is then laminated on the quantum well structure layer 14Cin the organic metal vapor phase deposition device. Manufacture of thelight-emitting body 10 is then completed by laminating a metal backinglayer 18 on the cap layer 16 by transferring to an evaporation device.

It should be noted that, although in the example described above,trimethyl gallium (Ga(CH₃)₃: TMGa) is used as the Ga source, trimethylindium (In(CH₃)₃: Than) is used as the In source, and monosilane (SiH₄)is used as the Si source, other organic metal raw materials (such as forexample triethyl gallium (Ga(C₂H₅)₃: TEGa), triethyl indium (In(C₂H₅)₃:TEIn) etc) and other hydrogen compounds (such as for example disilane(Si₂H₄) etc) could be employed.

It should be noted that, although in the example described above, anorganic metal vapor phase deposition device was employed, it would alsobe possible to use a hydride vapor deposition device (HVPE) or molecularbeam epitaxial (MBE) device. Also, since the deposition temperaturesdepend on the devices used in the tests, there is no restriction to thetemperatures described above. Furthermore, although InGaN was used as anexample of the buffer layer 14A, a suitable choice could be made fromnitride semiconductor materials containing N as the chief group Velement and including at least one or more of In, Al or Ga as group IIIelements for the buffer layer 14A.

Also, although the film thicknesses of the above layers and the dopingamounts of the Si are not restricted to the amounts illustrated in theexamples described above, the amounts described above are more suitable.Furthermore, although an example was described in which a GaN layer 14Bwas laminated on the buffer layer 14A in the example described above,apart from GaN, it would be possible to make a suitable selection fromnitride semiconductors containing N as the chief group V element andincluding at least one or more of In, Al or Ga as group III elements andhaving a band gap that is transparent with respect to the light emissionwavelength of the quantum well structure 14C. The example describedabove was an example in which the GaN layer 14B and InGaN/GaN quantumwell structure layer 14C were doped with Si, but there is no restrictionto this, and it would be possible to dope these with other impurities(such as for example Mg), or, if required, not to perform doping.

Next, an electron beam detector 20 employing a light-emitting body 10 asdescribed above will be described.

FIG. 6 is an axial cross-sectional view of an electron beam detector 20.In this electron beam detector 20, a light-emitting body 10 thatconverts incident electrons to fluorescence and an light incident face Iof a photodetector 30 are optically coupled through an optical member(optical guide member) 22. Also, the electron beam detector 20 isintegrated by physical connection of the light-emitting body 10 and thephotodetector 30 through the optical member 22. More specifically, theoptical member 22, which is made of material that is transparent to thefluorescence, is stuck onto the light incident face I, and thelight-emitting body 10 is mounted on this optical member 22. The opticalguide member 22 may be a light guide such as an optical fiber plate(FOP), or, apart from this, could be a lens that focuses thefluorescence generated by the light-emitting body 10 onto the lightincident face I.

A fluorescence-transparent adhesive layer (adhesive: resin) AD2 isinterposed between the optical member 22 and the photodetector 30, sothat the relative position of the optical member 22 and photodetector 30is fixed by the adhesive layer AD2.

The optical member 22 is a glass plate and an SiN layer ADa and SiO₂layer ADb are formed on the rear face 12 b of the substrate of thelight-emitting body 10, the SiO₂ layer ADb and glass plate of theoptical member 22 being melt-bonded. Since the SiO₂ layer ADb and theglass plate are both silicified oxides, these can be melt-bonded byheating. Also, although the SiO₂ layer ADb is formed on the SiN layerADa using for example a sputtering method, a high bonding force betweenthese is achieved.

Although the SiN layer ADa is likewise formed on the surface of thelight-emitting body 10 by for example a sputtering method, a highbonding force between these is achieved, so, as a result, the adhesivelayer AD1 sticks the light-emitting body 10 to the optical member 22.Also, since the SiN layer ADa also functions as a reflection-preventingfilm, this SiN layer ADa suppresses reflection in the direction of thelight-emitting body 10 of fluorescence generated in the light-emittingbody 10 in response to incidence of an electron beam. The overallrefractive indices of the adhesive layers AD1 and AD2 are respectively1.5.

In an electron beam detector 20 having such a structure, fluorescencegenerated in the light-emitting body 10 in response to incidence of anelectron beam enters the optical member 2 through the adhesive layer AD1which is made of fluorescence-transparent material, and reaches thelight incident face I of the photodetector 30 by successive transmissionthrough the optical member 2 and adhesive layer AD2.

The photodetector 30 illustrated in this example is a photo-multiplier.This photodetector 30 comprises a side tube 30 a made of metal, anoptical input window (faceplate) 30 b that blocks the aperture at thehead of the side tube 30 a, and a vacuum enclosure comprising a stemplate 30 c that blocks the aperture at the bottom of the side tube 30 a.Within this vacuum enclosure, there are arranged a photo-cathode 30 dformed on the inside face of the optical input window 30 b, an electronmultiplier 30 e and a positive electrode A.

The optical input face I is the external face of the optical inputwindow 30 b; fluorescence that is incident at the optical input window Ipasses through the optical input window 30 b to enter the photo-cathode30 d and the photo-cathode 30 d emits (photo)electrons in the directionof the interior of the vacuum enclosure by performing photoelectricconversion in response to incidence of fluorescence. These electrons aremultiplied by the electron multiplier 30 e comprising a microchannelplate or mesh type dynode and are collected by the anode A.

The electrons that are collected by the anode A are extracted to outsidethe photodetector 30 through pinholes 30 p formed through the stem plate30 c. A plurality of pinholes 30 p are provided, and a prescribedpotential is supplied to the electron multiplier 30 e through thesepinholes 30 p. The potential of the metal side tube 30 a is 0V, and thephoto-cathode 30 d is electrically connected with the side tube 30 a.

In an electron beam detector 20 as described above, there is provided alight-emitting body 10 having a response speed and intensity of lightemission that are fully satisfactory for application to a scanningelectron microscope or mass spectroscope and having an excellentpersistence rate, so high-speed response and excellent life performancecan be achieved.

The electron beam detector 20 can be used in a scanning electronmicroscope (SEM) or mass spectroscope.

FIG. 7 is a diagram given in explanation of major parts of a scanningelectron microscope. The scanning electron microscope comprises theelectron beam detector 20. When an electron beam e1 is directed onto asample SM and the surface of this sample SM is scanned by this electronbeam e1, secondary electrons are emitted from the surface of the sampleSM and these are directed to the electron beam detector 20 as anelectron beam e2. An electrical signal is output from the pin holes 30 pin response to incidence of the electron beam e2.

Specifically, this scanning electron microscope is a device wherein animage of a sample SM is picked up by providing at least thelight-emitting body 10 of the electron beam detector 20 within a vacuumchamber (not shown), and scanning the surface of the sample SM arrangedin this vacuum tube with an electron beam e1, directing the secondaryelectrons generated from the sample SM by this scanning into theelectron beam detector 20, and correlating in synchronized fashion theposition of scanning of the electron beam e1 and the output of theelectron beam detector 20. The scanning speed in this scanning electronmicroscope in which the electron beam detector 20 is adopted can thus begreatly increased, since the response speed of the light-emitting body10 of the electron beam detector 20 is of nsec order. Also, since thelight-emitting body 10 has an excellent persistence rate, performancesuch as the life property of this scanning electron microscope issignificantly improved.

FIG. 8 is a diagram given in explanation of major parts of a massspectroscope.

This mass spectroscope comprises an electron beam detector 20 asdescribed above. When a suitable potential is supplied to the apertureAP and negative potential is applied to the first dynode DY1 positionedon the opposite side to the separating section AZ with respect to theaperture AP, positive ions located in the separating section AZ passthrough the aperture AP and collide with the first dynode DY1 andsecondary electrons produced by the collision are released from thesurface of the first dynode DY1 and these secondary electrons aredirected to the electron beam detector 20 as an electron beam e3.

It should be noted that, when negative ions are extracted from theseparating section AZ by applying a positive potential to the seconddynode DY2, these negative ions collide with the second dynode DY2,causing secondary electrons to be released from the surface of thesecond dynode DY2 due to this collision and these secondary electronsare then directed to the electron beam detector 20 as an electron beame3. An electrical signal is then output from the pinholes 30 p inresponse to incidence of the electron beam e3.

There are various types of mass spectroscope but in all cases ions areseparated time-wise or spatially in accordance with their mass.

Assuming that the separating section AZ is a flight tube, the time ofpassage of the ions through the interior of the flight tube differsdepending on their mass, so their arrival times at the dynode DY1 or DY2are different; consequently, the masses of the ions can be distinguishedby monitoring the change with time of the current value if that isoutput from the pinholes 30 p. That is, this current value indicates theamount of ions of the respective masses in each time.

Assuming that the flight path of the ions changes in accordance withmass depending on the magnetic field in the separating section AZ, theions passing through the aperture AP will be different for each mass,and this can be controlled by varying the magnetic flux density in theseparating section AZ; the masses of the respective ions can thereforebe distinguished by monitoring the change with time of the current valuethat is output from the pinholes 30 p. Specifically, the amounts of ionsof the respective masses are indicated in each time by the currentvalue, by sweeping the flux density or scanning the position of theaperture AP.

As described above, a mass spectroscope as described above comprises: avacuum chamber (not shown) in which is arranged at least a chemicalsemiconductor substrate 1 of an electron beam detector 20; a separatingsection AZ that separates the ions that are generated from a sample (notshown) in this vacuum chamber in spatial or time-wise fashion inaccordance with their mass; and a dynode DY1, DY2 that is irradiatedwith the ions that are separated by the separating section AZ: massanalysis of the aforesaid sample is conducted in accordance with theoutput of the electron beam detector 20 after directing to the electronbeam detector 20 the secondary electrons e3 generated from the dynodeDY1 or DY2 in response to incidence of ions on the dynode DY1 or DY2.Thus, in a mass spectroscope in which the electron beam detector 20 isadopted, the response speed of the light-emitting body 10 of theelectron beam detector 20 is high, being of nsec order, so the massanalysis capability can be very greatly improved. Also, thelight-emitting body 10 has an excellent persistence rate, so performancesuch as the life performance in this mass spectroscope is significantlyimproved.

The present invention is not restricted to the embodiment at describedabove and can be modified in various ways. For example, the nitridesemiconductor layer 14 may be partially of quantum well structure, ormay be entirely of quantum well structure. Also, the photodetector 30,apart from being a photomultiplier, could be for example an avalanchephotodiode (APD). Furthermore, the optical member 22 is not restrictedto being of linear shape, but could be of curved shape, and its sizealso could be suitably altered.

Industrial Applicability

The present invention can be utilized in a light-emitting body thatemits light in response to incidence of electrons, and an electron beamdetector, scanning electron microscope or mass spectroscope using this.

1. A light-emitting body that emits fluorescence in response toincidence of electrons said light-emitting body comprising: a substrate;a nitride semiconductor layer having a quantum well structure formed onone of faces of said substrate, said nitride semiconductor layer beingcomprised of In_(x)Al_(y)Ga_(1-x-y)N and In_(a)Al_(b)Ga_(1-a-b)N, where,x≦1, y≦1, x+≦1, a≦1, b≦1, a+b≦1; a cap layer formed on said nitridesemiconductor layer, said cap layer having an electron incidence face,said cap layer being comprised of AlGaN; and a metal backing layerformed on the cap layer.
 2. The light-emitting body according to claim1, wherein said nitride semiconductor layer is comprised of InGaN andGaN.
 3. The light-emitting body according to claim 1, wherein athickness of said metal backing layer is at least 800 nm.
 4. Thelight-emitting body according to claim 3, wherein a thickness of saidcap layer is not more than 10 nm.
 5. The light-emitting body accordingto claim 1, wherein a well width of the quantum well structure is notmore than 4 nm.
 6. An electron beam detector comprising thelight-emitting body of claim
 1. 7. The electron beam detector accordingto claim 6, further comprising a photodetector having sensitivity forthe fluorescence generated by said light-emitting body.
 8. A scanningelectron microscope comprising: the electron beam detector of claim 7;and a vacuum chamber in which at least said light-emitting body isarranged, wherein an image of a sample is picked up by scanning asurface of the sample arranged in said vacuum chamber with an electronbeam, thereby directing secondary electrons generated from the sample tosaid electron beam detector, and then correlating a scanning position ofthe sample and output of said electron beam detector.
 9. A massspectroscope comprising: the electron beam detector of claim 7; a vacuumchamber in which at least said light-emitting body is arranged; aseparating section for separating in spatial or time-wise fashion theions generated from a sample in the vacuum chamber in accordance withmass of the ions; and a dynode that is irradiated with ions separated bysaid separating section, wherein secondary electrons generated from saiddynode in response to incidence of ions on said dynode are directed tothe electron detector, and mass spectroscopy of the sample is performedfrom output of said electron beam detector.